Naldemedine

What naldemedine is and how it works

Naldemedine is a prescription medicine that blocks opioid receptors specifically in the gut, without crossing into the brain in most people, to relieve constipation caused by opioid pain medicines -- without reducing the pain-relieving effect of the opioid. (1) (2)

Naldemedine carries two genuine risks that need medical supervision: a risk of tears (perforation) in the gut wall in people with certain bowel conditions, and a risk of opioid withdrawal symptoms in people whose blood-brain barrier is not working normally. Tell your clinician about any bowel disease or brain/nervous system condition before starting.

Mechanism of action: how naldemedine works

Naldemedine is a derivative of naltrexone conjugated to a side chain that limits central nervous system penetration, giving it peripherally restricted mu-, delta-, and kappa-opioid receptor antagonism predominantly within the enteric nervous system, which reverses opioid-induced reductions in GI motility without reversing centrally mediated analgesia in patients with an intact blood-brain barrier. (1) (2)

What naldemedine is used for

Before taking naldemedine

Do not take / not appropriate for

• Do not take naldemedine if you have a known or suspected blockage in your bowel (gastrointestinal obstruction), or a condition that makes a blockage likely to come back -- there is a risk of the bowel wall tearing (perforation). (all countries) (1) (2)
• Do not take naldemedine if you have had a serious allergic reaction to it before. (all countries) (1) (2)
• Naldemedine is not recommended during pregnancy or breastfeeding, because it could trigger opioid withdrawal in a baby whose mother takes opioids regularly. (United Kingdom, European Union) (2)

Tell your clinician about

• Any bowel condition such as diverticular disease, peptic ulcer disease, Crohn's disease, a bowel cancer, or previous bowel surgery -- these raise the risk of a serious bowel-wall problem.
• Any brain or nervous-system condition, such as a brain tumour, cancer that has spread to the brain, active multiple sclerosis, or advanced Alzheimer's disease -- these can affect the barrier that normally keeps naldemedine out of the brain, raising the risk of opioid withdrawal.
• Whether you have severe liver disease.
• All other medicines, especially other opioid-blocking medicines or anything that strongly affects liver enzymes (CYP3A4).
• Whether you are pregnant, planning pregnancy, or breastfeeding.

How to take naldemedine

• Taken once daily, by mouth, with or without food.
• Can be taken with or without a laxative.
• Try to take it at the same time each day.
• Do not change your dose or stop taking naldemedine without your clinician's guidance -- if you stop your opioid pain medicine, tell your clinician, since naldemedine is usually stopped at the same time.

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3)

Missed dose

If you miss a dose, contact your clinician or pharmacist for guidance, or take your next dose at the usual time. Do not double up doses.

Overdose

Seek urgent medical attention if you think you have taken too much naldemedine, especially if you develop severe abdominal pain or signs of opioid withdrawal. (1)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Serious warnings

Interactions

• Other opioid antagonist medicines should generally be avoided together with naldemedine. (1)
• Strong CYP3A4-inhibitor medicines (such as itraconazole, ketoconazole, ritonavir, or clarithromycin) can raise naldemedine levels -- your clinician may want closer monitoring. (2)
• Strong CYP3A4-inducer medicines (such as rifampicin, carbamazepine, or phenytoin) can substantially lower naldemedine levels and reduce how well it works -- these combinations are generally avoided. (2) (1)

Pregnancy, breastfeeding, kidney/liver function, age

Monitoring

Before starting

• Review for bowel conditions that raise perforation risk
• Review for brain/nervous-system conditions that could disrupt the blood-brain barrier
• Confirm ongoing opioid use and expected duration

During treatment

• Watch for severe, persistent, or worsening abdominal pain.
• Watch for symptoms of opioid withdrawal, especially in patients with blood-brain-barrier-disrupting conditions.
• Reassess need for naldemedine if the underlying opioid pain medicine is stopped.

Storage

Store tablets at room temperature in their original packaging, out of reach of children, following the exact instructions on your product's label.

Frequently asked questions

References

1. SYMPROIC (naldemedine) tablets for oral use -- full prescribing informationU.S. Food and Drug Administration / DailyMed (NIH), full prescribing information, Shionogi Inc. · United States · accessed 2026-07-30 · source 1
2. Rizmoic 200 microgram film-coated tablets -- Summary of Product Characteristicselectronic medicines compendium (emc), United Kingdom -- Shionogi/Viatris marketing authorisation holder · United Kingdom · accessed 2026-07-30 · source 2
3. Rizmoic (naldemedine) -- EPAR medicine overviewEuropean Medicines Agency (EMA) -- EPAR for Rizmoic · European Union · accessed 2026-07-30 · source 3

Brand names by country

Single-ingredient naldemedine names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries